Heat-developable light-sensitive materials are well known in the art. Examples of heat-developable light-sensitive materials and heat development processes are described, for example, in Shashinkogaku no Kiso, "Edition of Higin-en Shashin", pages 242 to 255 (Corona Co., Ltd., 1982) and U.S. Pat. No. 4,500,626.
With respect to processes for obtaining positive color images many methods have been produced. For instance, in U.S. Pat. No. 4,559,290, a method is described wherein an oxidized compound, which in its oxidized state does not have a dye releasing ability, obtained by converting a so-called DRR (dye releasing redox) compound, :s coexistent with a reducing agent, the reducing agent is oxidized by exposed silver halide upon heat development, and the oxidized compound is reduced with remaining reducing agent which is not oxidized, whereby a diffusible dye is released. Further, in European Patent 220,746A and Kokai Giho 87-6199 (Kokai Giho, Vol. 12, No. 22), a method of forming a heat-developable positive image using a novel compound which can release a diffusible dye in a similar mechanism is described.
However, the above described positive image forming methods are disadvantageous in that, while a portion of the reducing agent is oxidized upon the reduction of silver halide, the reducing agent which is not oxidized and remains at the exposed area in case of using a short period of developing time reduces the reducible dye providing compound to cause the increase in the minimum density.